Centrifugal fluid devices or centrifuges are well known. Since the late 1960's centrifugal-fluidic systems have been developed and used for integrated and automated processing, in particular for analytic and diagnostic applications [Norman G. Anderson. Computer interfaced fast analyzers. Science, 166 (3903): 317-324, 1969; Norman G. Anderson. Analytical techniques for cell fractions. XIV. Use of drainage syphons in a fast-analyzer cuvette-rotor. Analytical Biochemistry, 32 (1): 59-69, 1969.]. Applications of such devices include the separation of substances. In a reference frame spinning with the rotor, the centrifugal force points away from the centre of rotation. If multiple phases are present in a channel, the laws of buoyancy teach that the denser phases settle towards the radially outer part of their container, thus displacing the less dense phases to the radially inwards part. This promotes the movement of low-density constituents towards the axis of rotation. More dense constituents of the fluids are forced to move radially outwardly under the influence of the centrifugal force.
The centrifugal field also induces a radially oriented hydrostatic pressure gradient in fluid-filled channels, containers or chambers. Fluid volumes subjected to a centrifugal field therefore tend to flow in the planes oriented perpendicular to the axis of rotation.
Such development has led to systems providing a micro-fluidic lab on a chip and/or μTAS (Micro Total Analysis System) and technologies developed since the beginning of the 1990's relate to centrifugal based “Lab on a disk” systems. [C. T. Schembri, Vth Ostoich, P. J. Lingane, T. L. Burd, and S. N. Courts. Portable simultaneous multiple analyte whole blood analyzer for point of care testing. Clinical Chemistry, 38 (9): 1665-1670, 1992; C. T. Schembri, T. L. Burd, A. R. Kopf-Sill, L. R. Shea, and B. Braynin. Centrifugation and capillarity integrated into a multiple analyte whole blood analyzer. Journal of Automated Methods & Management in Chemistry, 17 (3): 99-104, 1995; M. J. Madou and G. J. Kellogg. LabCD: A centrifuge based microfluidic platform for diagnostics. In G. E. Cohn and A. Katzir, editor, Proceedings of SPIE—System & Technologies for Clinical Diagnostics & Drug Discovery, volume 3259, pages 80-93, 1998.].
These devices are well known as analysis tools. In a first application the centrifuge is used to process, e.g. separate the fluid in accordance with the density of the constituents of the fluid. The analysis methodology will include a first step of exposing the fluid to a centrifugal force and then, once separation has been achieved, analyzing the sample, i.e. the rotation and the analysis are taken in two separate sequential steps. In a second arrangement, an external sensor is used to analyse the fluid during its rotation. However, as the sensor is not in the same frame of reference, i.e. it is provided in an inertial (lab) frame as opposed to the (rotating) reference frame, it is not possible to continuously interact with the fluid during the rotation of the fluid on the centrifugal device. In such a scenario there is a difficulty of discontinuous sampling at a finite frequency, i.e. with a single stationary detector the sampling occurs at most once per rotation of the fluid. A further difficulty arises in that the sensor is physically separate from the centrifuge. In the known arrangements, this physical separation is required to allow for rotation of the centrifuge as physical contact between the external sensor and the substrate within which the fluid container is defined would restrict the movement of the substrate. Apart from the discontinuous nature of the interaction of a fluid in a rotating chamber with a stationary component, the communication, e.g. of optical signals, through a gap commonly has a negative effect, e.g. regarding signal strength, background noise and overall quality.
There is therefore a need for an improved centrifugal based device.